Sorghum's Reputation As Water-Saving Crop Confirmed

As water becomes scarce and more expensive to pump in the High Plains, more farmers are likely to turn to grain sorghum as a main crop. That is due to the fact that sorghum is more drought tolerant than corn and produces higher yields during moderate to severe drought conditions.

But there are some questions than need answering before farmers commit to sorghum such as yield response to deficient irrigation, decided Susan O'Shaughnessy, a USDA Agricultural Research Service engineer. Farmers also have questions about whether to plant early-maturing varieties, which are planted later and are thus less vulnerable to drought, or late-maturing varieties that have higher yields but only if they are given enough moisture.

O'Shaughnessy set up field trials using early- and late-maturing sorghum varieties produced under four deficit irrigation conditions. Those conditions included applying water to meet 80%, 55%, 30% and 0% of the crop's water-replenishment levels. "You could consider the 80% replenishment level to be mild deficit irrigation, and the lower replenishment levels to be moderate to extreme deficit irrigation," O'Shaughnessy explains.

O'Shaughnessy and her colleagues planted the late-maturing variety in late May or early June and the early-maturing crop in late June. Both crops were harvested at about the same time in the fall.

They grew the crops for three seasons, tracked weather data and rainfall levels, and measured evapotranspiration rates, which is an indicator of the plant's overall water needs.

The researchers found that over the three growing seasons of their evaluation, water-use efficiency (the water used by the crop in relation to the crop yield) was typically greatest at the 55% replenishment level. But even a 30% replenishment at least doubled the yields when compared with no irrigation.

At 80% replenishment, the late-maturing variety consistently produced higher yields than the early maturing one. But the early-maturing variety produced sufficient yields to make it a viable alternative if a farmer has limited well capacity or if a crop planted earlier in the season (such as corn or cotton) has failed because of hail, floods, or drought.